1. Field of the Invention
The present invention relates to an exposure apparatus and exposure method used when producing a semiconductor integrated circuit, a liquid crystal display element, a thin film magnetic head, or another microdevice or a photomask by photolithography and to a microdevice and photomask produced using such an exposure apparatus.
2. Description of the Related Art
In photolithography, one step in the production of a microdevice, use is made of an exposure apparatus for projection exposure of an image of a pattern of a photomask or reticle (hereinafter referred to as a xe2x80x9creticlexe2x80x9d) on to a substrate for exposure (semiconductor wafer or glass plate coated with a photoresist). The reticle itself used for such an exposure apparatus is sometimes produced using an exposure apparatus. In the following explanation, when necessary to differentiate between the two, the former will be referred to as a xe2x80x9cdevice exposure apparatusxe2x80x9d and the latter as a xe2x80x9creticle exposure apparatusxe2x80x9d.
In such an exposure apparatus, the substrate on which the pattern is to be transferred and formed is loaded on a substrate stage by a transport system having a robot arm etc. and held by a holder provided with a plurality of support pins provided on the substrate stage. The positions at which the substrate is supported by the support pins are set to be near the outer circumference of the substrate so as not to damage the portion of the substrate on which the pattern is to be formed or are set to positions giving the minimum flexing of the substrate due to its own weight.
When simply placing a substrate on such support pins, the speed and acceleration of movement would be limited as it is necessary to prevent the positional deviation of the substrate accompanying step motion of the substrate stage. This would make the time required for movement longer and the throughput (production per unit time) lower. Therefore, the practice has been to form suction ports in the centers of the support pins for suction by negative pressure (vacuum) and to hold the substrate carried on the support pins by the support pins by applying negative pressure for suction through the suction ports.
Further, the practice has been to check if a substrate is loaded on the support pins by processing the record of operation of the exposure apparatus by a computer or by visual confirmation by the operator. In apparatuses applying a negative pressure to the substrate for suction, sometimes this is checked by detection by a pressure sensor of the change in the pressure when a substrate is being held by suction and not being held by suction.
When producing for example an ordinary reticle by such an exposure apparatus, however, a light blocking layer comprised of chrome (Cr) or another material not passing much light is formed on the surface of the glass substrate for reticle production (blank), so almost none of the exposure light passes through the substrate and there is not that much of a problem. When producing a special reticle such as a phase shift reticle (including a Shibuya-Levenson type, half tone type, and chromeless type) using a light blocking layer passing light to a certain extent, however, the exposure light passes through the substrate and is reflected at the surface of the support pins supporting the substrate and at the sample table and other structures present beneath the substrate. The reflected light exposes the exposure layer (photoresist) formed by coating on the substrate surface and sometimes cause a deterioration of the line width uniformity of the pattern or uniform deviation of the line width from the target line width.
Further, when the substrate is transported by the transport system, if dust etc. is deposited on the substrate supports of the robot arm or other portions with which the substrate comes into contact, this dust etc. will sometimes end up depositing on the substrate. In this case, if the substrate is supported by the support pins with the dust etc. in between them, the de facto height of the support pins will change and, along with this, the state of flexing of the substrate will differ individually. Therefore, for example, there is the problem that it is no longer possible to sufficiently eliminate error due to flexing using a correction value found in advance for the case of ideal flexing of the substrate due to its own weight and error will occur in the shape of the pattern formed. Further, the flatness becomes poor and the amount of the leveling operation increases which sometimes cause a fall in the throughput.
Further, in an apparatus in which the substrate is simply placed on the support pins, as explained above, the throughput falls, while in an apparatus in which the substrate is subjected to negative pressure for suction, the substrate is sometimes damaged by the suction and the substrate flexes locally by a large amount at the suction portions, so correction is difficult and a high accuracy pattern sometimes cannot be formed.
Further, for detecting if a substrate is present on the support pins, in a configuration applying negative pressure to the substrate for suction, the presence of a substrate is detected by detecting the pressure, but this cannot be done when not using a configuration applying negative pressure for suction. Further, in an apparatus where the presence of the substrate is detected by processing the record of operation of the transport system by computer or by visual confirmation by the operator, the reliability is poor and sometimes substrates are doubly loaded.
A main object of the present invention is to enable the production of a high accuracy, high quality photomask or microdevice.
Another object of the present invention is to enable the reliable detection of whether a substrate has been loaded onto a holder.
According to a first aspect of the present invention, there is provided an exposure apparatus, for exposing a substrate through a mask on which a pattern is formed, provided with three first support members for supporting the substrate substantially horizontally at three locations outside of illuminated areas of the substrate.
The xe2x80x9cilluminated areasxe2x80x9d in this case means the pattern area at which the pattern is mainly formed and alignment mark areas (areas where alignment marks are formed) or information mark areas (areas where marks comprised of a bar code, matrix code, letters, numerals, symbol, etc. where identification information and other various information are set are formed). That is, the pattern area is the area which is illuminated by the exposure light. An alignment mark area is an area which is illuminated for optical detection of the position of the alignment mark, while an information mark area is an area which is illuminated for optical detection of the information concerned.
Since the substrate is supported by the first support members at three locations outside the illuminated areas of the substrate, even when the substrate to be exposed is a light transmitting substrate (for example, a substrate for producing a phase shift reticle), the light passing through the substrate is not reflected by the first support members to expose the exposure layer of the substrate surface. Therefore, the line width uniformity of the pattern no longer deteriorates and the line width no longer deviates uniformly from the target line width and therefore a high accuracy pattern can be formed. Further, since the substrate is supported at three points, stable support can be realized.
The positions at which the substrate is supported by the first support members are preferably set to positions in an area outside the illuminated areas giving the minimum flexing of the substrate. This is because the smallest amount of flexing possible is advantageous in processing for correction of flexing.
Alternatively, the positions at which the substrate is supported by the first support members are preferably set to positions other than positions against which second support members supporting the substrate at the time of transport of the substrate abut. By setting the positions in this way, even when dust etc. deposited on portions of the second support members which the substrate contacts deposits on the substrate, since the positions of support by the first support members differ from the positions of support by the second support members, the flexing state of the substrate is not affected by the dust etc. Therefore, the substrate flexes ideally by its own weight and it becomes possible to reliably eliminate error due to flexing using a correction value found in advance for the case of ideal flexing of the substrate due to its own weight. Therefore, less error occurs in the shape of the pattern formed. Further, there is no longer an increase in the amount of the leveling operation and a decline in the throughput can be prevented.
In this case, it is possible to have the substrate supported at three points by the second support members and arrange the first support members and the second support members so that when one vertex of a first triangle formed by the first support members is designated as a first vertex, the side formed by the two vertices other than the first vertex is designated as a first base, one vertex of a second triangle formed by the second support members is designated as a second vertex, the side formed by the two vertices other than the second vertex is designated as a second base, the first base and the second base are substantially parallel, the first vertex is positioned at the second base side with respect to the first base, the second vertex is positioned at the first base side with respect to the second base, and parts of the first triangle and the second triangle overlap, the first vertex becomes substantially equal in distance from the two vertexes forming the second base and the second vertex becomes substantially equal in distance from the two vertexes forming the first base. It is therefore possible to prevent interference when the substrate is transferred from the second support members to the first support members and realize stable transfer.
In this case, preferably the surface roughness of the surface of the first support members abutting against the substrate, for example, the center axis average roughness, is set to not less than 0.1 xcexcmRa. By setting it to such a surface roughness, the coefficient of friction between the substrate and the first support members becomes larger and the holding property of the substrate can be improved. Therefore, it is possible to increase the speed and acceleration of the step motion of the substrate to a certain extent and possible to improve the throughput. Further, since the substrate is moved at a certain speed even without being held on the first support members by suction by negative pressure etc., it is possible to prevent damage to the substrate accompanying suction by negative pressure and local flexing.
Further, it is possible to form at least the surfaces of the first support members abutting against the substrate (portions including the surfaces) by one of diamond, sapphire, ruby, and ceramic. The first support members as a whole may be formed by such materials or the first support members may be formed by providing a coating layer of such a diamond or other material on the surface of a base material of another material.
The surfaces of the first support members against which the substrate abuts (tip surfaces) may be made substantially circular and, in consideration of the surface roughness and material of the tip surfaces and the maximum speed and maximum acceleration of the substrate, the diameter set to 0.5 to 30 mm or so so as to prevent the substrate from shifting on the first support members.
The apparatus should desirably have an anti-reflection member provided under the substrate to prevent light reflection. Unless the anti-reflection member is thus provided, the light having passed through the substrate would be reflected by a structure such as the sample table on which the first support members are provided to cause the accuracy of the pattern sometimes to deteriorate as in the above. By providing such an anti-reflection member, however, the light passing through the substrate is absorbed by the anti-reflection member and less reflected light is produced, so this problem is solved.
The apparatus can further be provided with a moving body supporting at a plurality of places a substrate holder having the three first support members. In this case, the substrate holder should desirably be kinematically supported at three points different in position from the three first support members. The xe2x80x9ckinematic supportingxe2x80x9d refers herein to a manner of supporting which will provide a restriction in at least one direction in a horizontal plane. For example, there are provided at one of the substrate holder and the moving body hemispherical projections corresponding to vertexes of a triangle while there are provided at the other of the substrate holder and moving body a conical concavity, V-shaped concavity and flat surface corresponding to the hemispherical projections, respectively.
The apparatus is preferably further provided with a sensor for optically detecting if a substrate is supported by the first support members. This enables reliable detection of the presence of a substrate and enables prevention of double loading of substrates etc.
In this case, when the substrate is formed to a substantially rectangular shape, it is possible to adopt a sensor having a light emitter for outputting detection light and a light receiver for receiving the detection light from the light emitter and to arrange the light emitter and the light receiver so that the detection light strikes one surface of the substrate at an angle of about 45xc2x0 in the state with the substrate supported by the first support members. At this time, preferably a corner of the substrate is used as much as possible so that the detection light does not reach the illuminated areas of the substrate. The wavelength of the detection light is different from the wavelength of the exposure light for transfer of the pattern, but this is to reduce as much as possible the effect on the exposure layer of the substrate surface.
According to a second aspect of the present invention, there is provided an exposure apparatus, for exposing a substrate through a mask on which a pattern is formed, provided with a moving body having a plurality of supports whose surfaces abutting against the substrate have a surface roughness of 0.1 xcexcmRa or more. The area of each of the supports which abuts against the substrate should desirably be substantially circular and have a diameter of about0.5 to 30 mm. Also, the moving body may be adapted to support, at a plurality of places, the substrate holder having the plurality of supports. Further, the moving body may be adapted to kinematically support the substrate holder at places different from those of the plurality of supports.
According to a third aspect of the present invention, there is provided an exposure apparatus, for exposing a substrate through a mask on which a pattern is formed, provided with a substrate holder on which the substrate is placed, and a moving body supporting the substrate holder substantially horizontally at three locations. In this case, the substrate holder should desirably be kinematically coupled on the moving body.
Further, while not particularly limited to this, in the exposure apparatuses according to the first to third aspects of the present invention, the mask may be a master mask and the substrate may be a mask substrate for producing a working mask. In this case, it is possible to enlarge the pattern for transfer, divide the pattern thus obtained into a plurality of parent patterns, and transfer reduced images of the parent patterns obtained by a projection optical system on a plurality of areas with surroundings partially overlapping on the mask substrate.
In the above exposure apparatuses according to the first to third aspects of the present invention, the mask may be a master mask and the substrate may be a mask substrate for producing a working mask. In this case, each of the apparatuses may further be provided with an alignment mechanism for aligning the substrate, before exposure of the substrate, using reference positions the same as at least three reference positions to be used for alignment of the working mask in another type of exposure apparatus (device exposure apparatus) in which the working mask produced using the exposure apparatus (reticle exposure apparatus) is to be used.
Since the external references of the substrate used when transferring and forming a pattern to the substrate are made the same as those of the working mask (substrate) used for alignment in another exposure apparatus where the working mask produced using this substrate is to be used, there occurs less error than in the case of alignment using different external references and therefore it is possible to improve the positional alignment between the master mask and the other substrate to be exposed by the other exposure apparatus (called the xe2x80x9cdevice substratexe2x80x9d for convenience in differentiating it from the substrate of the working mask) and as a result possible to form a pattern with a high accuracy on the device substrate.
According to a fourth aspect of the present invention, there is provided a microdevice produced using an exposure apparatuses provided according to any of the first to third aspects of the present invention.
According to a fifth aspect of the present invention, there is provided a device producing method including a lithography step in which an exposure apparatus provided according to any of the first to third aspects of the present invention is used.
According to a sixth aspect of the present invention, there is provided a photomask produced using an exposure apparatus provided according to any of the first to third aspects of the present invention.
According to a seventh aspect of the present invention, there is provided a photomask producing method including a lithography step in which an exposure apparatus provided according to any of the first to third aspects of the present invention.
According to an eighth aspect of the present invention, there is provided an exposure method for exposing a substrate through a mask on which a pattern is formed, the method including exposing the substrate being held substantially horizontally at three locations outside of illuminated areas of the substrate.